The invention relates to a new process for demineralizing and decolorizing fruit juice and must.
The production of sugars from fruit juices, in particular from grape juice and must, on a large industrial scale is gaining increasing importance. Depending on the climatic conditions in the various growing regions, fruit juice or must contains, for example, 17 to 20% by weight of sugar, 0.6% by weight of protein, about 0.3% by weight of fats and about 130 mequivalents of salts/1. The fruit juices or musts moreover have a greater or lesser content of dyestuffs, predominantly anthocyanins.
To produce sugar from fruit juices, for example pear juice and grape juice or must, these have to be decolorized and demineralized. The juices or musts have to date been demineralized by ion exchange, that is to say by treatment with strongly acid cation exchangers in the H.sup.+ form and weakly basic anion exchangers in the amine form. During the demineralization, or more precisely when flowing through the weakly basic anion exchangers, decolorization occurs at the same time as the absorption of the acids.
This demineralization and decolorization by ion exchange has the disadvantage that the dyestuffs are absorbed almost irreversibly onto the weakly basic anion exchangers and are therefore removed to only a small degree during regeneration with sodium hydroxide solution and thus block the anion exchanger groups which participate in the exchange. That is to say, the usable capacity of the weakly basic anion exchangers employed in this process decreases greatly after only a few working cycles; in addition, the washing out properties of the anion exchangers deteriorate.
To protect the weakly basic anion exchangers, the demineralization filters of strongly acid cation exchangers and weakly basic anion exchangers have already been preceded with filters packed with specific strongly basic decolorizing resins. However, these decolorizing resins were also deactivated so severely by the dyestuffs after only a few working cycles that they had to be purified by expensive treatment with oxidizing agents.
This means that the known processes for decolorizing and demineralizing fruit juices, in particular grape juice and must, by ion exchange have the disadvantage that the lives of the anion exchangers are too short and/or they require expensive processes for purification of the anion exchangers.
Surprisingly, it has been found that decolorization and demineralization of fruit juices, such as pear juice and grape juice and must, can be achieved effortlessly and without consumption of ion exchangers if the juice or must is chromatographed on charged cation exchangers. Surprisingly, it has been found that during chromatography of the juices on strongly acid charged cation exchangers, the dyestuffs are not held in the ion exchanger but migrate virtually quantitatively with the salts into the electrolyte first runnings. In contrast to the separation of molasses into sugars and non-sugars by the electrolyte first runnings process, in which only incomplete removal of the dyestuffs from the sugar is achieved, when the process is used for the separation of sugars and non-sugars (salts) in fruit juices, almost quantitative separation of the dyestuffs from the sugars is achieved.